The present invention relates generally to a process for the recovery of an economically valuable concentrated iron product, useful as the feedstock for the iron and steel making processes, from industrial waste streams typically comprising heavy materials, such as iron oxide, cadmium, zinc and lead, and light materials, such as lime and ash. A waste materials stream comprising iron oxide, cadmium, zinc, lead, silica, lime and ash, such as electric arc furnace (EAF) dust or blast furnace dust, is subjected to a combination of steps including compaction, separation of the iron oxide from other materials in the waste materials stream by flotation or magnetic separation either before or after compaction, roasting the materials in a reduction furnace, such as a rotary hearth furnace, and crushing the roasted materials. The other materials in the waste stream from which the iron oxide is separated also can be treated further to recover other chemical and metal values, as disclosed below.
During the process, fumes and other wastes are exhausted which typically comprise lead, zinc and cadmium. These fumes and other waste can be processed by a baghouse or/and by a wet scrubber or other capturing device. The captured materials can be recycled to a recovery process wherein the captured materials are introduced into a leaching process which causes the zinc, cadmium, and lead constituents to go into solution while the iron and iron oxide which was not removed during the separation process remains undissolved. Any undissolved iron and iron oxide can be recycled to the process of the present invention, specifically to the compacting step.
There exists a need for a method which will allow the recovery of an iron product from industrial waste streams which can be subjected to further treatments, resulting in a relatively pure iron product, such as direct reduced iron, and/or a very pure iron product, such as pig iron, which can be used as the feedstock for other processes, such as a steel making process. The industrial waste streams of most interest for this invention include a typical electric arc furnace waste and basic oxygen furnace streams and the particulate matter filtered or otherwise removed from various substeps of the invention, particularly from the fumes of a reduction furnace, such as a rotary hearth furnace, or from the small scale blast furnace or cupola furnace. Producing an iron product with a minimum amount of impurities, such as zinc ferrite, lead and cadmium, is advantageous because the iron product can be used as the feedstock for steel production processes.
A method which results in the recovery of an iron product has additional value in that the iron product can be sold for use in other processes. Furthermore, recovery and retreatment of exhaust and other waste products from the present invention and from other processes and subprocesses has a beneficial effect on the environment, and a beneficial, economic effect on the cost of the steel making process. The exhaust may be further processed by filtering it through a bag house to capture the particulate materials, and then subjecting the captured materials to leaching to recover the iron and iron oxide which was not separated out during the separation step. The iron materials then can be compacted and sent to a reduction furnace or a blast furnace.
Iron is smelted, or refined, in a furnace in which iron ore, coke and limestone are heated. Scrap iron also can be used as a feed to the iron smelting furnace. Prior to introducing scrap iron to the furnace, it is de-scaled of iron oxide, or rust. The mill scale, as it is called, is a waste product typically disposed of and not used in the iron production process. Steel is basically an iron alloyed with other chemical elements. Scrap steel also can be used as a feed in the making of steel. Mill scale also is not used in the steel production process. Finding an economical and/or beneficial use for this mill scale would provide iron and steel mills an opportunity to dispose of the mill scale. Likewise, used batteries provide a waste disposal problem. Used batteries also are not typically used in the steel making process. Rather than disposal in a landfill, it generally is preferable to recycle the used batteries, which are rich in iron oxide. Finding an economical and/or beneficial use for used batteries would reduce the quantity of such material sent to landfills and provide a recycle for usable components. All of these iron oxide rich materials can be added to the waste stream feed which is fed into the present process.
As can be seen, there exists a need for a method which separates iron oxide from other materials contained in a waste stream and processes the iron oxide to create DRI and/or pig iron and which will allow exhausts and fumes from reduction or pig iron furnaces or the like to be filtered in a baghouse or/and a wet scrubber so that the iron oxide which was not recovered during the separation step can be recovered by leaching the captured materials and recycled back to the process of the present invention. This need is addressed by the present invention.